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owtap - Packet sniffer for the owserver protocol


owtap -p owtap-tcp-port -s owserver-tcp-port



1-wire is a wiring protocol and series of devices designed and manufactured by Dallas Semiconductor, Inc. The bus is a low-power low-speed low-connector scheme where the data line can also provide power.

Each device is uniquely and unalterably numbered during manufacture. There are a wide variety of devices, including memory, sensors (humidity, temperature, voltage, contact, current), switches, timers and data loggers. More complex devices (like thermocouple sensors) can be built with these basic devices. There are also 1-wire devices that have encryption included.

The 1-wire scheme uses a single bus master and multiple slaves on the same wire. The bus master initiates all communication. The slaves can be individually discovered and addressed using their unique ID.

Bus masters come in a variety of configurations including serial, parallel, i2c, network or USB adapters.

OWFS design

OWFS is a suite of programs that designed to make the 1-wire bus and its devices easily accessible. The underlying priciple is to create a virtual filesystem, with the unique ID being the directory, and the individual properties of the device are represented as simple files that can be read and written.

Details of the individual slave or master design are hidden behind a consistent interface. The goal is to provide an easy set of tools for a software designer to create monitoring or control applications. There are some performance enhancements in the implementation, including data caching, parallel access to bus masters, and aggregation of device communication. Still the fundemental goal has been ease of use, flexibility and correctness rather than speed.


owserver (1) is the backend component of the OWFS 1-wire bus control system. owserver (1) arbitrates access to the bus from multiple client processes. The physical bus is usually connected to a serial or USB port, and other processes connect to owserver (1) over network sockets (tcp port).

Frontend clients include a filesystem representation: owfs (1) , and a webserver: owhttpd (1) . Direct language bindings are also available, e.g: owperl (3) .

There are also many light-weight clients that can only talk to owserver (1) and not to the 1-Wire bus directly. They include shell and multiple language modules (perl, Visual Basic, python,...)

owserver protocol

All the owserver (1) clients use the owserver protocol for communication. The owserver protocol is a well documented tcp/ip client/server protocol. Assigned the "well known port" default of 4304.


owtap (1) is interposed between owserver (1) and clients, to display and help resolve communication problems. Network communication is forwarded in both directions, but a visual display is also created, with statistics and "drill-down" of individual packets.

Specific Options


TCP port or IPaddress:port for owtap
Other OWFS programs will access owtap via this address. (e.g. owdir -s IP:port /)


TCP port or IPaddress:port for owserver
The tcp port (IP:port) for the "upstream" owserver.


If owserver (1) is started:
owserver -p 4304 -d /dev/ttyS0
owserver on tcp port 4304 and connects to a physical 1-wire bus on a serial port.

You can directly query owserver (1) with
owdir -s 4304 /

To see the protocol in action:
owtap -s 4304 -p 3000
owdir -p 3000 /

In this case owtap (1) is connecting to owserver (1) on the original port (4304) and offering a new port (3000) for clients.


owtap (1) is a pure Tcl/TK program and will run whereever Tcl/TK is available (Windows, Macintosh, Linux, Unix)


owserver protocol


See Also


owfs (1) owhttpd (1) owftpd (1) owserver (1) owdir (1) owread (1) owwrite (1) owpresent (1) owtap (1)

Configuration and testing

owfs (5) owtap (1) owmon (1)

Language bindings

owtcl (3) owperl (3) owcapi (3)


DS1427 (3) DS1904(3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417 (3)


DS2401 (3) DS2411 (3) DS1990A (3)


DS1982 (3) DS1985 (3) DS1986 (3) DS1991 (3) DS1992 (3) DS1993 (3) DS1995 (3) DS1996 (3) DS2430A (3) DS2431 (3) DS2433 (3) DS2502 (3) DS2506 (3) DS28E04 (3) DS28EC20 (3)


DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)


DS1822 (3) DS1825 (3) DS1820 (3) DS18B20 (3) DS18S20 (3) DS1920 (3) DS1921 (3) DS1821 (3) DS28EA00 (3) DS28E04 (3)


DS1922 (3)


DS2450 (3)


DS2890 (3)

Multifunction (current, voltage, temperature)

DS2436 (3) DS2437 (3) DS2438 (3) DS2751 (3) DS2755 (3) DS2756 (3) DS2760 (3) DS2770 (3) DS2780 (3) DS2781 (3) DS2788 (3) DS2784 (3)


DS2423 (3)

LCD Screen

LCD (3) DS2408 (3)


DS1977 (3)


DS2406 (3) -- TAI8570



Paul Alfille (

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